Radiant heaters adapted to glass-ceramic cooking hobs that comprise an insulating base on which is arranged at least one electrical resistor and a temperature-limiting device that includes a sensor that is arranged on the electrical resistor are known in the state of the art, the limiting device being switched on when the sensor detects inside the radiant heater a pre-set limit temperature, with the result that the radiant heater is switched off until the sensor of the temperature-limiting device detects inside the radiant heater a temperature lower than the reset temperature of the automatic switch, time after which the radiant heater is supplied once more in order to provide the required power.
One of the problems associated to this type of radiant heater is that when the temperature-limiting device switches on, the radiant heater switches off, giving the user the impression that it is defective, as it switches on and off cyclically, controlled by an ON/OFF switch for the obtaining of the required power, and also creating the false impression that the radiant heater is cold. To solve the latter problem some radiant heaters, such as the one described in U.S. Pat. No. 7,268,324 B2, include electronic monitoring means that includes a switch adapted to switch on a lighting device. The lighting device remains switched on for a period of time after the radiant heater has been disconnected, with the result that the temperature of the glass-ceramic hob falls to a temperature at which the user may touch it without any danger of being burned.
In U.S. Pat. No. 6,057,529 the radiant heater comprises a temperature-limiting device that includes an expanding rod or pipe that acts as a sensor member, and a switch device that includes five terminals in contact with the expanding rod or pipe. Initially, the rod connects the first and second terminal, and the third and fourth terminals to each other respectively, with the result that when the radiant heater is connected a lighting device lights up to indicate that the radiant heater is on. When the temperature-limiting device switches on, the rod expands and disconnects the third and fourth terminals from each other, connecting the fourth and fifth terminal to each other. The connection between the fourth and fifth terminal is maintained during the connection/disconnection cycles of the temperature-limiting device, it being disconnected when the rod contracts after the measured temperature has dropped to a temperature that does not represent a danger to the user.